I'd guess a non-profit project with such small, incidental, reverent-without-being-misleading image reuse can wait until they receive a souvenir cease-and-desist letter, if ever, before worrying about the rights issues.

That suit supports the idea the project can wait for communication from the rightsholder at negligible risk. (That is, there's no need for ad hoc copyright warnings from third-party non-experts.)

To wit: this is a lawsuit of choice, initiated by a plaintiff (backed by the EFF) who had material briefly taken-down by a DMCA notification. The studio didn't sue: it only sent a take-down, then was itself sued. The studio doesn't appear to be seeking damages, even though the alleged-infringing video has now been up for years (post-counter-notify, with more than 1.2 million views). The studio just wants the take-down honored and the lawsuit dismissed.